Ceramic foams have a number of applications including filtering and refractory uses. Unfortunately ceramic foams are difficult to produce. Generally, such foams have been produced by incorporating into the ceramic a material which would be lost on sintering, such as saw-dust or a wax. Such processes produced porous ceramic materials but were time consuming, and expensive.
U.S. Pat. No. 4,374,202issued Feb. 15, 1983 assigned to R. M. Industrial Products Company discloses a process for making a foamed refractory. An aqueous dispersion of binder, ceramic fiber and filler is frothed and then heated to set the foam. The resulting green ceramic foam may then be sintered. This art does not teach a process which may be used with less than 50 percent of ceramic fiber. Furthermore, the disclosure does not clearly teach the use of "gelling agents" to set the foam.
The Derwent abstract of Japanese Patent JP 52019768, discloses applying a PVC emulsion containing a blowing agent to a surface of a ceramic and foaming the PVC. The foam does not contain any ceramic material. Rather, a flexible foam is applied to a preformed ceramic material. The present invention contemplates the manufacture of a foamed ceramic.
There are several proposals to impregnate a preformed foam material with ceramic material and then to burn out the foam. Generally, the foam is a urethane. Representative of this type of art are the Derwent abstracts of Japanene Patents JP 54085209 and JP 52077114.
Chemical Abstract 85:193774S of DE 2,606,957 to Jensen et al teaches incorporating a ceramic material into a wet foam of a ceramically, hydraulically, or chemically setting material such as a urea resin. The present invention does not contemplate the use of the urea type resins as disclosed in CA 85:193774S.
EP 0 211 575 published 25-02-87 in the name of The Babcock and Wilcox Company discloses a foamed refractory product produced by chemically foaming a mixture of ceramic fibers, elastomer, and a solvent. The present invention contemplates the use of an aqueous based ceramic mixture, which does not contain solvent, to produce a green ceramic foam. Additionally, the present invention contemplates compositions which do not contain materials which react with acid to produce gas (e.g. blowing agents).
The present invention seeks to provide a process for making a porous, foamed, green ceramic, from an aqueous based ceramic compound.